Human mesenchymal stromal cells (hMSCs) are an interesting source for cell therapies and tissue engineering applications, because these cells are able to differentiate into various target tissues, such as bone, cartilage, fat and endothelial cells. In addition, they secrete a wide array of growth factors and cytokines that exert immunomodulatory and trophic effects on surrounding cells. A large number of clinical trials is currently employed to investigate the use of MSCs and these trophic/immunomodulatory effects. The differentiation of hMSCs towards the osteogenic lineage is controlled by several signal transduction pathways, amongst which the cAMP/PKA pathway, but its exact role is still incompletely understood. In this thesis we show that activation of this pathway in hMSCs with the small molecules dibutyryl-cAMP (db-cAMP) and forskolin result in osteogenic differentiation, whereas treatment of these cells with a second cAMP analogue (8-br-cAMP) resulted in adipogenic differentiation. We observed differences in the PKA activation patterns as well as in genetic profiles, but the precise mechanism underlying these different effects on differentiation remain to be elucidated. For bone tissue engineering applications, the differentiation of MSCs towards the osteogenic lineage prior to implantation, is generally believed to account for enhanced bone formation. Here, we demonstrated that the differentiation of hMSCs induced by db-cAMP not only resulted in enhanced in vitro osteogenic differentiation and in vivo bone formation, but also resulted in enhanced secretion of bone specific growth factors, such as insulin-like growth factor 1 and bone morphogenetic protein 2. Furthermore, conditioned medium derived from these db-cAMP-treated cells induced proliferation and differentiation of fresh cells, demonstrating a trophic effect of these factors. To investigate how the secretome of hMSCs can be modulated further, a high throughput screen based on the hypoxia responsive element (HRE) was developed and by using this assay, we identified phenanthroline as a novel hypoxia mimic that is able to shift the hMSC secretome towards a trophic angiogenic profile. These data demonstrate that, besides their direct differentiation, hMSCs can be ‘trained’ to secrete specific growth factors for specific applications that can be induced by treatment with small molecules, but also by i.e. scaffold modifications.
|Award date||17 Feb 2012|
|Publication status||Published - 17 Feb 2012|